President Obama announced a series of new policies yesterday intended to reduce fuel consumption and greenhouse gas emissions, capping a week of widespread changes aimed at reversing the legacy of George W. Bush.

In his first seven days in office, Obama has banned the use of controversial CIA interrogation tactics, ordered the closure of the U.S. military prison camp at Guantanamo Bay, Cuba, and begun planning for the drawdown of troops in Iraq. He also imposed stringent limits on lobbyists, unveiled an $825 billion stimulus plan, and ordered a halt to any last-minute rules and regulations put in place by his predecessor.

The moves are part of an effort by Obama to follow through on his campaign promise to forge a new direction in Washington, administration officials said. "What you have seen in the first week is rapid change and a resetting of our global agenda," said White House press secretary Robert Gibbs. "The president believes we can't afford to continue what we are doing. We can't afford to slow down."

Yet despite such ambitions, Obama and his aides are also facing a stark reality: Rolling back eight years of the Bush administration is not going to happen overnight.

Obama's call for tougher vehicle emissions standards, for example, ran into immediate opposition from major business and auto industry groups. His plan to close the Guantanamo Bay prison has angered Republicans who object to transferring suspected terrorists to U.S. facilities. Many of those same Republicans are also fighting his economic stimulus proposal, arguing that it is too costly and would ultimately be ineffective, while others have attacked his plan to quicken the pace of troop withdrawals from Iraq.

The new administration has created some dilemmas of its own, as well. After Obama announced strict new lobbying limits for political appointees last week, the White House conceded it would have to issue a waiver for William J. Lynn III, a former Raytheon lobbyist who is up for a post at the Pentagon.

"Governing is a lot more complicated than campaigning," said Peter Wehner, a former Bush aide who is now a senior fellow at the Ethics and Public Policy Center, a conservative think tank. "He's the candidate who has presented himself as moving the Earth. . . . When you set those kinds of expectations, it's tough to pull them back."

Administration defenders note that Obama won election handily in November and that he has some of the highest approval ratings of any new president in modern times. With that kind of popularity, they argue, he is in a position to push for the kind of dramatic changes promised during the campaign.

Obama and his aides and have worked to tamp down expectations, especially regarding the economy. In his inaugural address, Obama warned that "the challenges we face are real" and "will not be met easily or in a short span of time."

At the same time, he also has suggested that he has no intention of lowering his sights. "There are some who question the scale of our ambitions, who suggest that our system cannot tolerate too many big plans," Obama said during the Jan. 20 speech. "Their memories are short, for they have forgotten what this country has already done, what free men and women can achieve when imagination is joined to common purpose and necessity to courage."

In addition to his early moves on intelligence policy, the environment and the economy, Obama lifted a ban on U.S. funding for international family planning groups that perform abortions, which was first put in place by Ronald Reagan and revived by Bush. The new president also vowed to open more federal records to public scrutiny and named former U.S. senator George J. Mitchell as a special envoy for Middle East peace.

The rapid-fire actions are an early down payment on promises he made throughout his presidential campaign. As he fought his way through a bruising Democratic primary, Obama assailed Bush's economic policies as tax cuts for the wealthy, mocked the president's lack of stature around the world and hammered his response to Hurricane Katrina and his handling of the Iraq war.